The present invention relates to a resin-molded semiconductor device, and more specifically to a resin-molded axial lead-type semiconductor device.
Semiconductor devices have been extensively used which are obtained by sealing in an epoxy resin a sub-assembly in which a semiconductor pellet is held by brazing between a pair of axial leads. So far, however, the sub-assembly is sealed in the epoxy resin by using a metal mold. When a glass is to be used for the purpose of sealing, a slurry of glass is applied round a semiconductor pellet in the sub-assembly and is then baked. In this case, there is no need of employing the metal mold. When the epoxy resin is used, however, the metal mold must be employed unlike the case of using the glass. The reason for requiring the metal mold is because there is no one-can-type epoxy resin available which cures to some extent within a few minutes. Namely, the resin initially is transformed into a sol just before the resin cures, and its viscosity decreases strikingly relative to its viscosity at ordinary temperature. Accordingly, the resin separates from the sub-assembly.
Japanese Patent Laid-Open No. 1174/1980 discloses a method according to which the sub-assembly is sealed in a glass, and the epoxy resin is further applied thereto. In this case, however, the applied epoxy resin forms a film which is not thick enough to achieve the desired sealing.
According to a sealing method which is now practiced by using an epoxy resin, it is necessary to employ a metal mold. Therefore, cumbersome operation is required for setting the sub-assembly within the metal mold, for injecting the epoxy resin therein, for parting the sub-assembly from the metal mold, and the like. In particular, it is difficult to continuously perform the setting and parting operations, thereby imposing a bottleneck for mass-production. When a parting agent is contained in the epoxy resin to facilitate the parting operation, the adhesiveness between the resin and the leads is reduced, and gaps are often formed between the leads and the sealing layer in the semiconductor device. Water infiltrates through the gaps and reaches the semiconductor pellet; i.e., the semiconductor device loses desired characteristics and further loses reliability in operation.